To seek out animal models for human genetic skin diseases. Such mutations have occurred spontaneously or been produced in various animal production laboratories; some in our own animal laboratories at NIH. Animals are bred either by heterozygote or homozygote matings. Some of the animals are kept in germ-free conditions, especially those that present immunologic defects. Tissues from these animals are studied by light and electron microscopy, by immunofluorescence, and by chemical and microbiological techniques.